Apparatus for direction finding



.Buly 12, 1949. m. o. McCARTHY ETAL 2,75,975

APPARATUS FOR DIRECTION FINDING Filed April 15, 1946 2 Sheets-Sheet l INVENTOR.

THOMAS o. MCCARTHY am) 'AQTl-IUQ 12 DAV/5 I 4 v ATTORNEY .Buiy 12, 1949, T. o. MCCARTHY EFAL 2,475,75

APPARATUS FOR DIRECTION FINDING Filed April 15,1946 2 Sheets-Sheet 2 INVENTOR. THO/{4A5 0; MCCARTHY EYQND ARTHUR P. DAV/5 ATTOPA/EY Patented July 32, i

Thomas 0. McCarthy, United States Navy, and Arthur ll. Davis, New York, N. Y.

Application April 15, 1946, Serial No. 662,130 2 Claims. (o1. 343-113) This invention refers to an apparatus for determining direction, and more particularly to a combination magnetic, visual, and radio direction finder.

An object of this invention is to provide a single, compact and portable device by means of which visual and radio bearings can be individually or simultaneously determined and simultaneously referred to and correlated with a magneticcompass bearing.

Another object is to provide a compact and portable device by means of which'the direction of a radio radiating structure may be determined with respect to magnetic north.

Another object is to provide means whereby the magnetic compass can be maintained in a substantially level position while in use and thus permit free operation of its moveable element.

Another object is to provide a portable device of the type herein described which can be readily carried to and used at any suitable location where visual, magnetic, and electrical interferences are at a minimum.

Another object is toprovide a device as described herein which may be readily carried and supported by the observer, while in use, in such position and accessibility as will enable convenient and ready use and operation of its bearing determining elements and control members, and

at the same time insure efiective response by sight and sound.

Another object is to provide a combination of diflerent facilities whereby visual, radio, and magnetic bearings can be correlated during periods of daylight or darkness.

Another object is to provide in a single instrument a plurality of direction-determining facilities of such a nature that at least two of them will be operative during periods of inclement weather.

Another object is to provide a portable unitary I apparatus capable of being carried, and used while being carried, by the observer.

Further objects and advantages of this invention, as well as its construction, arrangementand operation will be apparent from the following description and claims in connection with the accompanying drawing, in which:

Fig. 1 is an elevation view, partly insection showing the various direction determining e l e-' ments of the device.

Fig. 2 is a schematic wiring diagram of a circuit that may be used with the device, together with a characteristic responsegraph of the receptor element.

'Fig. 3 shows the device as carried by the observer while in use.

As shown in Fig. 1, a telescopic sight consisting of enclosing tube ill, of any suitable non-magnetic material but preferably or metal, is provided with an apertured eyepiece l l, an open end I2, and a centering pin f3. Secured to tube In, by any suitable means, is a magnetic compass, generally indicated as It, and consisting of any suitable material of any suitable design but preferably of the simple liquid-damping type having a liquid chamber formed by the compass casing or housing 56 wherein the compass card i] may be supported on a pivot pin I8 and its abrupt motion retarded by the damping liquid,

closed and sealed against leakage by means of a cover glass 16a.

Angularly positioned intermediate the ends and within tube Ill at a slot or opening M is secured a supporting frame or-plate I8 to which there is secured a small mirror Ha which obstructs a portion of the inner diameter of the tube ill. The angular position of mirror Ida, and its purpose, is such as to direct a portion of the line of vision from eyepiece H down to the compass card ll while at the same time permitting a sufficiently unobstructed view of the object on which visual observations are to be made by means of open end I2 and object centering pin i3.

Located within tube I0 at a second slot l5, and

a suitable distance ahead of mirror lila, is a lens |5a obstructing not over one-half the diameter of tube II]. This lens is focused to provide accommodation for the observer's eye 66 when sighting is divided between the distant object 58 along sight-line 2!! and the magnetic-compass reading along sight-line 2! by means of mirror lfla. A suitable sliding cap 22, embracing tube iii, serves to secure lens [5a in place, permit of ready removal or replacement,' and exclude from the interior of the tube undesired external light. An air chamber 22' communicating with the liquid chamber of casing 55 is provided for the purpose of eliminating air bubbles from the liquid chamber as is well-known in the magnetic compass art.

Illumination of the compass card ll during darkness is provided by means of a small electric flashlight suitably mounted on tube to and in- .cludes housing- 123 containing a suitable dry cell,

kept in a substantially level position while in use. To enable the observer to maintainthe instrument in substantially levelposition a bubble-type spirit level '21 is secured to the compass housing or casing frame It at the position indicated with its longitudinal axis located in a horizontal plane at right angles to the longitudinal axis of telescope tube In near the. indicator'of the magneticcompass card l1, and within range of the light rays from fiashlight lens 25, where it can be simultaneously observed together with the magnetic bearing indicated on the compass card.

The apparatus thus far described-provides a portable unitary instrument for the accurate and simultaneous observation of visual and magnetic bearings which may be carried by the observer to any suitable location outside of the influence of magnetic structures and visual barriers.

The term portable as used throughout this description refers to equipment capable of use while being carried on the person of the observer.

Suitably attached to, and preferably at the open end of, telescope tube I is a radio direction finding receptor-coil swivel supporting bracket 28:: having a split head 28, tightening or securing screw 38 cooperating with thumb-nut 3i, and a lower portion 28 secured for relative rotary movement by means of screw 28b. A scale 28c enables the ,degree of relative displacement from the longitudinal axis of telescope tube i0 to be observed. This arrangement enables any differences between visual and radio hearings to be I noted. Suitably supported in bracket 28 is the receptor-coil supporting frame 82 and cap 33' of any suitable shape, in this case indicated as circular, preferably constructed of non-magnetic metal and having its electrical continuity interrupted by means of a slot 34 located at any suitable position and filled with suitable insulating material to exclude moisture and render desired mechanical support. The purpose of insulated slot 34 is to permit the'receptor coil supporting frame 32 and cap 33 to act as a shield and decrease the external capacity effects of receptor coil or winding 35 without preventing the receptor coil from picking upthe desired electromagnetic component of the arriving energy.

The ends of receptor-coil winding 35 and 35a are connected to suitable terminals 36 and 31 one of which may be grounded to the supporting frame bracket 28.

A suitable co-axial, or other-type cable 38 (Fig. 3) provided with suitable terminals 33 and to facilitate quick and easy connection and disconnection, may be used to connect the receptor coil 35 with the radio receiver 4|. Also, the outer conductor or shield of co-axial cable 38 can, for best results, be grounded to the coil supporting frame bracket 28 and to the casing of radio receiver 4! to insure good electrical conductivity between the bracket 28, coil frame. 32,

, closing cap '33, telescope tube I8, and the case of radio receiver 4i, so that the operator's body, when holding the instrument in operating position, will also become a part of the general grounding system and thus reduce electrical distortions to a minimum.

The center of gravity of the receptor coil and shielding structure is preferably located below the longitudinal axis of telescope tube IO' so as to aid in maintaining the telescope tube and magnetic compass in suitable level position when in use. A

Fig. 2. is a schematic wiring diagram of apparatus which may beused. It consists of receptor-loop winding connected to terminals 88 and 81 ieeding vacuum tube detector 33. shunted across the line-feeding vacuum tube 38 is a variable tuning condenser 42, and in series in the grid lead is the primary winding 43 of a variable coupling transformer, and a grid con-'- denser M. value is connected between the grid and cathode of vacuum-tube detector 38. The secondary winding 36 of the variable coupling transformer is connected in series with the plate of vacuumtube detector 53 and by means of coupling control ill permits the circuit to function for the reception of modulated currents (voice or music) with regenerative amplification, or if the coupling is still further increased vacuum-tube detector will go into a self-oscillation state by means oi. which continuous waves can be received and detected in the well-known heterodyne manner. A by-pass condenser 48 may be used, if; desired, to shunt the primary 49 of the audio amplifying transformer 4| and the platecurrent source 51.

Audio-amplifying-transformer secondary 58 is connected to the cathode and grid membersof amplifying vacuum tube 52 and its output is arranged to feed a suitable loud-speaker or other translating device 54 through a volume-control potentiometer or variable resistor 55. Energy for the anodes and cathodes of vacuum tubes 38 and 52 may be furnished from common sources of "A battery 56 and 13" battery 51. Any desirable number of stages of amplification or any suitable combination. of vacuum tubes or wiring system can be used as required or desirable. A Jack 59 is connected in parallel with loudspeaker 54 so that headphones maybe inserted in the receiving system when signals too weak properly to actuate the loud speaker are received. In making accurate determinations of the A grid leak 45 of suitable resistance direction in. which radio signals are arriving, the

minimum-energy-response position of receptor loop 35 can be used as indicated in the position shown where 58 is the radiating structure and. because of the figure of eight characteristic 53 and '60 of a coil receptor loop, the received energy will vary with rotation of the loop between the positions indicated by lines 6| and 62 to much greater extent than if the radiating source were located along line 63 and the loops rotation varied as indicated between lines -34 and 35, under which condition maximum energy response would prevail.

For unilateral direction determinations a plain antenna effect can also be added in a conventional manner to the system of Fig. 2 and thus the actual radio bearing can be distinguished from its reciprocal. I

Inv Fig. 3 is shown the arrangement of the device while in use and carried by the observer 55. With the telescope portion l8 raised to eye level the distant object 58 (Figs. 1 and 2) is bisected by centering pin 13 (Fig. 1) while the magnetic bearing of compass l4 and the aural null response of the receptor coil 35 within casing 32 and 33 are observed. Adjustment to the desired frequency is effected by means of control 42 on the radio receiver 4| while modulated or continuous wave reception is attained and regeneration controlled by means of control 41.

Volume can be altered by means of control 55.. Audible signals 3! will be emitted by the loudspeaker 55 and directed upward toward the observers ear.

In the event microwave frequencies are employed the loop or coil 35 can be replaced with a suitable reflector or focusing antenna, and a wave guide substituted for co-axial cable 38.

Joint reactions from distant objects on the various associated devices eliminate the time inaccuracies that may otherwise prevail if separate observations were made by the same or different observers from or upon a moving object such as, for example, a ship afloat, an airplane, or a moving celestial body.

The expression single or simultaneous observation as used herein is defined a observations made by one observer at the same instant on different response devices.

The term magnetic compass as used herein is defined as an indicating device actuated by terrestrial polar magnetism, or any substitute device of the gyro, or repeater, type.

It is a well-known fact that visual and radio bearings may vary due to refraction and that radio and magnetic bearings may vary because of interfering electric and magnetic fields;v

therefore when coincidence of all three is obtained, either directly or by means of correction factors, the accurac of direction is well established. Some of these conditions may occur for instance when light and radio waves are directed or reflected to earth from celestial bodies such as, for example, the moon, where refraction is at a maximum when the path of observation lies near the earth's horizon although not necessarily to the same extent for both visual light and radio waves because refraction appears to depend to an extent upon the frequency or wave length of the radiation involved.

For facility of support in a suitable operating and carrying position a shoulder strap 68 is attached to the receiver 4 I.

Some of the various results that can be accomplished by the device as shown and described in.- clude the following:

(a) Aboard ship the apparatus can be carried to and used on the person of the observer away from the detrimental influences of stays, masts, and other obstructions and radiating structures.

(b) At sea, in dense forests or elsewhere, the magnetic bearing of radio-radiating structures can be accurately determined by means of simultaneous observations of the direction of arriving radio waves asreferred to the earth's magnetic field, regardless of conditions of visibility.

(c) The accuracy of the bearing of radiations from radio radiating structures with respect to the visual bearing can be determined.

(11) The deviation of magnetic north with respect to visual and radio bearings of radiating structures can be readily determined.

(e) The observers position with respect to two radio-radiating structures, or one radio-radiatin; structure and one visible structure, and magends of said tubular i; netic north can be determined by observation and triangulation.

(f) Small boats such as carried by naval vessels can operate at night and in conditions of low visibility using radio signals of a distinctive character radiated by the mother ship or by radiating stations on the beach or on other ships; either by determining the correct compass course and steering that course by this device or by using the radio signal in the manner of a homing device.

(g) Guard boats going from ship to ship at a fleet anchorage, can steer for any ship radiating a distinctive signal either by determining the correct compass course to steer by the compass on this device. or by utilizing the radio receptive feature as a. homing device.

(h) Men operating ashore, under cover of darkness or low visibility, can keep orientated and know the direction of a radiating station such as could be carried in a small boat or on landin craft and can, by this means, guide themselves to such a station. 5

Various modifications and changes can be made in the above-described apparatus without departing from thespirit and scope of this invention as set forth in the appended claims.

What is claimed is:

1. A portable direction finding instrument comprising, in combination, an optical telescope including a tubular body part having an eyepiece end and an objective'end, a magnetic compass depending from and supported by said tubular body part at a portion thereof intermediate the part, a radio receptor loop rotatably supported by said telescope substantially at the objective end thereof, a radio receiver adapted to be detachably connected to said loop, and a shoulder strap supporting said re-- ceiver on the person of the user.

2. The instrument defined in claim 1 wherein said receptor loop is secured for rotative motion relative to said telescope with the center of gravity of said loop normally below said telescope.

THOMAS O. McCARTI-IY. ARTHUR P. DAVIS.

REFERENCES CITED The following referenices are of record in the file of this patent:

UNITED STATES PA'I'ENTS in low visibility identify and 

